Nanoindentation Analysis for Local Properties of Ultrafine Grained Copper Processed by High Pressure Torsion

Abstract

Severe plastic deformation (SPD) techniques have recently been developed for producing bulk ultrafine grained metallic materials. High pressure torsion (HPT) produces finer microstructures than those achieved by other SPD processes because of the higher imposed strain and hydrostatic pressure. It is known that HPT-processed metals show a highly heterogeneous microstructure not only along the radius due to the nature of torsional deformation but also through the thickness. Since the sample size for HPT is small, the local properties of HPT-processed specimens have not been investigated yet. In this paper, we propose a method to obtain stress-strain curves from nanoindenting curves by combining the finite element method and the recursion method. The nanoindentation technique was employed to elucidate the local mechanical properties, especially the stress-strain behavior. The method to extract the stress-strain curves from the load-displacement curves obtained by nanoindentation tests was applied to the edge region of the HPT-processed sample. The extracted properties correlated well with experimental results qualitatively.